Bellevue Downtown Tunnel

2020 CMAA Project Achievement Award
Transportation: Construction value greater than $50 Million
Bellevue Downtown Tunnel

Owner: Sound Transit  |  CM: McMillen Jacobs Associates

The team was constructed using the Sequential Excavation Method (SEM). It was the first East Link project issued for Sound Transit and posed a significant construction risk. Soft ground tunneling by SEM is uncommon in the United States, and anticipated ground conditions left no room for error.

With the challenges at project start, the project team recognized the way to succeed was to: 
1.    Think innovatively, listen to every suggestion, and explore all options
2.    Understand project success will need to be a team effort
3.    Be a fair partner in all negotiations

The  team worked with Sound Transit, Atkinson, and the Engineer of Record (EOR) to effect several significant changes—all accomplished while maintaining a high standard of tunnel construction.
After bids were opened, roundtable meetings were held to discuss value engineering options. MJ led several in which it was decided to revise the SEM construction method from six-headings to the contractor-preferred three-headings for half the tunnel length. This allowed Atkinson to accelerate average baseline production from 3.2 ft/day to over 4 ft/day, and in some areas, 6 ft/day. 

During construction, several value engineering improvements were made, including elimination of pipe canopy support on the North Portal, allowing the follow-on E335 Contract to continue construction of the Bellevue Downtown Station without interrupting its work for E330 to install the canopy. Several requirements were eliminated as well, including prescriptive installation of tunnel pre-support, only allowing it where necessitated by the ground. 

The team also investigated new technologies and materials, leading to use of macro-synthetic fiber in the shotcrete reinforced concrete, and spray-applied waterproofing in the tunnel. Both had not been widely utilized in the U.S. Also, shotcrete, not a common permanent lining, was placed in the enlarged tunnel section where the emergency fans are located. 

These measures resulted in a cost savings to Sound Transit of over $2.7 million and establishment of a 30 days of Owner Control Float bucket. With this proactive and open construction management style, the CMC team facilitated an additional $2 million savings in unused toolbox items during SEM construction.